1. Field of the Invention
The present invention relates to a fuel cutoff valve and a breather pipe. The fuel cutoff valve is attached to an upper portion of a fuel tank and opens and closes a connection conduit for connecting inside of the fuel tank with outside. The breather pipe is provided in the fuel tank for connecting the inside of the fuel tank with the outside,
2. Description of the Related Art
A connection conduit for letting the fuel vapor off to a canister is conventionally provided in an upper portion of a fuel tank. A fuel cutoff valve is attached to the connection conduit. The fuel cutoff valve has a float that is placed in a valve chest and lifts up and down with an increase or a decrease of buoyancy by a variation in liquid fuel level. A valve plug for opening and closing a valve seat is provided above the float. The ascending liquid fuel level in the fuel tank increases the buoyancy of the float and lifts the float up integrally with the valve plug to close the connection conduit and interfere with the outflow of fuel.
The fuel cutoff valve of this structure functions as a full level detection device for detecting a preset full level in the course of fuel supply. The valve plug lifted up integrally with the float closes the connection conduit and increases the inner pressure of the fuel tank to automatically stop the fuel supply from a fuel gun. The detection position of the full level is generally the operation end position of the float and is thus significantly varied with a variation in flow rate of fuel supply. In a proposed fuel cutoff valve of a breather pipe type, the detection position of the full level is defined by the height of a lower opening end of a casing for receiving a float therein (see, for example, JP-A 11-229984).
In the prior art fuel cutoff valve of this proposed structure, the lower opening end of the casing has only a small contact area with the liquid surface of increasing fuel. The liquid surface of fuel gradually increases to the full level while occasionally being in contact with and occasionally being apart from the opening end. In the course of such fuel supply, the air is entrained from the air layer in the fuel tank into a casing CS as shown in FIG. 18. Namely the air is disadvantageously invaded into the casing CS.
Invasion of the air into the casing or more specifically into a valve chest, the liquid fuel flow is mixed with a large amount of the air. The large air content of the liquid fuel undesirably lowers the buoyancy of the float. This prevents the float from producing an adequate level of buoyancy.